Conventional line airplanes and multi-engine airplanes use at least two propulsion chains (6 for the larger airplanes, even 8 in the B52 or 10 in the B36), each having its own throttle lever. To pilot such airplanes, the pilot must be trained and qualified in multi-engine management.
Multi-engine training and qualification are costly, and can prove prohibitive for student pilots learning on multi-engine airplanes.
These days, there a few airplanes and helicopters that use distributed propulsion.
The Japanese aerospace exploration agency JAXA has for example developed an airplane in which the distributed propulsion is assured by several electric motors coupled in series to a single transmission shaft in order to actuate a single fan.
However, because of the presence of a single thrust member, any engine failure would not generate any imbalance in the flight of the aircraft from an aerodynamic point of view.
The Volocopter, the electric helicopter developed by the German company evolo, utilizes a propulsion architecture in which several engines are mounted in parallel, each being coupled to a propeller (rotor).
An engine failure in the Volocopter would necessarily induce an imbalance in the distribution of the lift of the aircraft, and would therefore necessitate the implementation of a specific engine management procedure by the pilot in order to maintain the control of the aircraft.
An engine failure can lead to a total shutdown of the engine or a lowering or reduction of its speed that can compromise the safety of the airplane and thereby that of the passengers and of the navigating crew, and more particularly during the critical take-off and landing phases.
One approach for limiting the impact of the total loss of the propulsion power is to duplicate the powertrains in an aircraft, one powertrain generally being composed of an engine, of a controller of the engine and of a propulsion force generation member of fan or propeller type.
A distributed propulsion in a two-seater aircraft for example is advantageous with electric motors having a high power density, dimensions which give them a lesser bulk, and suitable controllers.
In aircraft with distributed propulsion, a loss or a powertrain failure hardly ever means a loss of the overall propulsion of the aircraft.
Furthermore, a distribution of several propulsive members, such as propellers, on a wing makes it possible to increase the locale lift by virtue of the aerodynamic blast generated by the propellers, thus reducing stall speed of the aircraft.
However, these distributed propulsion architectures require complex piloting and management with a throttle lever for each engine in order to control the thrust imbalances. The pilots are therefore forced to apply difficult actions to manage the unbalanced thrusts in case of engine failure.
These days, developments in distributed propulsion constitute a key issue for the future of electrical aviation. The powertrain management avionics systems continue to be refined and optimized on an ongoing bases in order to automate and simplify the multi-engine piloting procedures.